Different methods for making such sulfonated coumarins are known, for example by the British patent GB 9 723 365 in the name of MOLECULAR PROBES which describes the synthesis of derivatives of 6,8-difluoro-7-hydroxycoumarin.
Thus, this patent notably mentions sodium 6,8-difluoro-7-hydroxycoumarin-4-methanesulfonate (compound no. 37).
Patent GB 9 723 365 also describes compounds resulting from a replacement of the hydroxyl group with a sugar remainder, the latter being therefore grafted on sulfonated coumarin. The reproduction of the grafting method described in the aforementioned patent is not valid for sulfonated coumarins since they are not soluble under the described conditions.